Many proposals have been made for generating electricity from tidal and other water flows, using hydrokinetic energy generation. A Policy Statement issued on Nov. 30, 2007 by the Federal Energy Regulatory Commission stated that “[e]stimates suggest that new hydrokinetic technologies, if fully developed, could double the amount of hydropower production in the United States, bringing it from just under 10 percent to close to 20 percent of the national electric energy supply. Given the potential benefits of this new, clean power source, the Commission has taken steps to lower the regulatory barriers to its development.” (FERC Policy Statement No. PL08-1-000). Initial proposals for hydrokinetic generation used turbine blades that were able to rotate under pressure from the flow of water. However, such systems were often only able to operate when the water was flowing in one direction. Even if energy could be generated from a tidal flow in both directions of flow, other significant issues arise because peak power flow is only available from a tidal flow at roughly 12-hour intervals. This can cause issues with maximum grid capacities needed to transmit the generated power. Storage devices to smooth out dispatch of power are desirable, but land requirements for the huge batteries, dual reservoir requirements for hydro storage and low efficiency of fuel cells have made known storage devices too expensive to be effective. Thus, known hydrokinetic devices have not been economically viable.
Generally, four types of hydrokinetic devices have been tested in recent years. These are: horizontal axis turbines, vertical axis turbines, oscillating hydrofoils and a Venturi system where water is accelerated through a “choke system” to create a pressure drop that can be used to drive turbines. One example of a vertical helical turbine generator is known from U.S. Pat. No. 6,036,443 to Gorlov. Gorlov discloses a vertically oriented helical turbine which includes helical airfoil-shaped blades that are arranged in a spiral about a central shaft. The helical arrangement allows the turbine generator to be used in multidirectional fluid flows. An array of the turbines can be provided to increase power output. U.S. Pat. No. 4,384,212 to Lapeyre discloses a horizontally mounted helical turbine that is used on the surface to translate surface wave energy into electrical energy. Another surface mounted helical generator is disclosed in U.S. Pat. No. 2,154,397 to Cook.
Significant issues are also caused by known devices to marine life, which can be harmed by the rotating turbine blades. Various proposals to reduce the damage to marine life includes encasing the turbine blades in a wire mesh cage, which adds to the expense of the installation and only act to protect larger animals such as turtles from coming into contact with the blades. However, the cages do nothing to prevent smaller fish from being harmed. Additionally, many proposed turbine blades can suffer damage from water-borne debris, and even shipping. Due to these problems, acceptance of hydrokinetic devices by local communities and environmentally aware groups has not been as strong as hoped for, and the reliability of the devices has been limited.
Most previous hydrokinetic generation proposals additionally involve providing a rigid housing or anchoring system to retain the generator. This can be prohibitively expensive, as it can involve anchoring installations, and also the installation of energy supply cabling and pipes. Additionally, once installed, there is typically not much flexibility to allow the turbines to move with different water flows. Various proposals exist to ameliorate these difficulties, including U.S. Pat. No. 4,849,647 to McKenzie discloses a floating helical turbine which is connected to a tether line by a flexible ball joint. U.S. Pat. No. 4,708,592 to Krolick et al. discloses a non-rigid helicoidal wind turbine that uses a flexible fabric sheet to form the helix, and which can be tethered to existing mast structures using swivel joints.
For the foregoing reasons, none of the suggested hydrokinetic energy devices have been successful in practice. Thus, there remains a need for an hydrokinetic energy generator that is efficient, can work in a variety of water flow situations possibly including an ice/water mix, and which does not harm marine life.